1. Field of the Invention
The present invention relates to lift trucks, and more particularly to lift trucks having boom-or-mast-supported claw-type handling elements with forks for handling elongate loads such as logs.
2. Description of the Prior Art
Existing load handling vehicles, such as the one shown in U.S. Pat. No. 3,669,293, typically have a pair of vertically disposed, laterally spaced apart, articulated claws pivoted to a boom.
However, the claws of known prior art load handling vehicles are interconnected and driven so that they operate only synchronously, not independently. Therefore, the claws of such vehicles cannot be manipulated independently of one another and the load handling capability of such vehicles is thereby limited.
Furthermore, the forks of both claws of such prior vehicles always remain parallel to each other. This makes it difficult to insert these forks under a load unless the load happens to be parallel to the plane of the forks. Consequently, it is hard to insert the forks under and pick up skewed or otherwise uneven loads such as logs in a haphazard pile. In addition, with such vehicles, it is difficult to unload logs onto a surface which is not parallel to the forks, such as the sloping bunks of a log truck parked on a hill. This occurs because each of the claws cannot be independently pivoted to adjust the attitude of each fork so that the load is approximately parallel to the support surfaces onto which it is to be loaded.
The claws of some prior load handling vehicles include a pivoted upstanding main carriage member, a lower forwardly extending fork member for supporting a load and an upper forwardly extending tusk which can be pivoted to grasp a load. However, limitations in the connection between the fork and main carriage member require that such members always maintain a constant angular relationship and prevent manipulation of the main carriage member while its fork remains stationary and supported from below. Therefore, the main carriage members and tusks cannot be used to reach forwardly and pull a load onto the forks while the forks remain supported in stationary positions to receive the load.
Moreover, although the tusks of some prior load handling claws are known to be pivoted independently of one another, the arcs through which such tusks can be pivoted are typically limited because of limitations of the tusk pivoting mechanism. For this reason, the tusks of such vehicles cannot be pivoted to grasp both very small and very large loads.
Furthermore, the boom or mast structure, the carriage heads, and hydraulic mechanisms of existing load handling vehicles commonly obstruct the line of sight from the operator to the load.
Load handling vehicles and carriage heads illustrative of the known prior art and of the foregoing problems are disclosed in U.S. Pat. Nos. 3,669,392; 2,997,193; 3,275,173; 3,125,234; 3,182,833; 2,958,434; 3,352,442; 3,034,821 and 3,817,567.